1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to optical time-domain reflectometry, and more particularly to optical time-domain reflectometry requiring fewer optical connections to a fiber under testing.
2. Description of the Related Art
Optical fibers and fiber networks are integral to modem communication systems. Testing of optical fibers is often accomplished by optical time-domain reflectometry, which sends optical signals into a fiber and analyzes reflections based on the timing and power of reflected signals. This information can be used to assess problems that an optical fiber or network may have due to poor connections, etc.
Existing optical time-domain reflectometers (OTDRs) have a number of ports for different uses, for example, one port for dark (out-of-service) testing, and one port for live (in-service) testing. This has several disadvantages. First, the device must be built with separate ports for live and dark testing, or perhaps even separate devices. Also, all available frequencies are typically not found on the dark port, so a dark fiber must be connected to both the dark and live ports in order for all wavelengths to be tested. Many OTDRs today use one port for multiple lasers and a single APD, for example 1310/1550/1625 nm. However, the existing OTDRs do not filter the received signal to multiple APDs so that the OTDR can function as both a dark and live fiber (out of band) OTDR from the same port.
Additionally, existing devices require a technician to use a passive optical network (PON) power meter to measure power levels in at the optical network terminal (ONT) (customer) location. If low or no power is detected, the OTDR live port is used to further troubleshoot the problem. Existing OTDR devices thus require the use of multiple devices, multiple ports, and multiple connections, which impedes efficient fiber optic network installation and servicing. Similarly some existing OTDRs combine a 1490/1550 nm PON meter on the same port with a single, unfiltered OTDR wavelength (e.g. 1550 nm or 780 nm). However, the no existing OTDR combines the PON meter with a live and dark fiber OTDR on the same port.